Torque detecting apparatus and electric power steering apparatus

ABSTRACT

A torque detecting apparatus which can detect steering torque applied on a steering shaft which connects a steering wheel and a steering mechanism from the steering wheel side and inverse input torque applied on the same from the steering mechanism side, and an electric power steering apparatus which can prevent deterioration of steering feeling when the inverse input torque acts, by driving and controlling the steering force assisting motor to cancel the inverse input torque. The torque detecting apparatus and the electric power steering apparatus judge that the inverse input torque is applied when a predetermined interrelation exists among a vehicle speed and angular velocities which are calculated at two positions distant in the axial direction of the steering shaft.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a torque detecting apparatus fordetecting steering torque applied on a steering shaft for steeringoperation, and an electric power steering apparatus for driving andcontrolling a steering force assisting motor based on the steeringtorque detected by the torque detecting apparatus.

[0003] 2. Description of the Prior Art

[0004] An electric power steering apparatus, which drives a steeringforce assisting motor based on detection result of steering torqueapplied on a steering wheel for steering operation and transmits turningeffort from the motor to a steering mechanism to assist steering, cancontrol assisting force characteristics according to a running state,such as vehicle speed and frequency of steering, more easily than ahydraulic power steering, which uses a hydraulic actuator as a source ofassisting steering force. Such an advantage has recently invited aninclination to allow wider application of the electric power steeringapparatus.

[0005] Such an electric power steering apparatus is under the necessityof detecting steering torque applied on the steering wheel. Thedetection is generally accomplished by detecting rotational angles attwo positions of a steering shaft which are distant in the axialdirection of the steering shaft, which connects the steering wheel andthe steering mechanism. Steering torque can be calculated based on adifference between the two rotational angles detected at said twopositions, since the difference corresponds to a torsion of the steeringshaft generated in the course of steering operation.

[0006] The steering shaft is constructed by connecting an input shaft onthe steering wheel side and an output shaft on the steering mechanismside through a torsion bar of a small diameter. Such a constructionallows a large rotational angle difference to arise according to thetorsion of the torsion bar between the input shaft and the output shaft,and accuracy of calculating steering torque can be increased bydetecting rotational angles of the two shafts respectively.

[0007] The present applicant has proposed, in Unexamined Japanese PatentPublication No. 2000-352502, a torque detecting apparatus in an electricpower steering apparatus which can preferably be used for detectingsteering torque. Said torque detecting apparatus has sensor unitsrespectively provided at connection parts of the input shaft and of theoutput shaft. The sensor units comprises magnetic targets, which areprovided in peripheral direction of an object rotational axis and tiltedapproximately equally against the axial direction of the steering shaft,and magnetometric sensors (MR sensors), which are provided on theexterior of the magnetic targets opposing the same and generates outputwhich changes as each target passes by.

[0008] In this construction, the magnetometric sensor in the sensorunits outputs voltage, which changes, as each target passes by, lineallywith a slope corresponding to the tilt of the targets set in peripheraldirection of the input shaft and the output shaft. The rotational anglesof the input shaft and the output shaft can be detected in non-contactmode based on the output from each corresponding magnetometric sensor.The steering torque applied on the input shaft by operating the steeringwheel is thus calculated based on the difference between the rotationalangles of the two shafts, which is obtained as an output differencebetween the magnetometric sensors corresponding to the input shaft andthe output shaft.

[0009] For controlling the steering force assisting motor in theelectric power steering apparatus, the magnitude of the steering torqueapplied on the steering wheel needs to be detected as well as thedirection of the steering torque, namely, whether the steering isperformed to the left or to the right. The torque detecting apparatusconstructed as described above judges the direction of the steeringtorque by comparing the rotational angle of the input shaft and that ofthe output shaft. The electric power steering judges that the steeringtorque is applied in the direction in which the input shaft precedes theoutput shaft.

[0010] In addition to the proper input torque (steering torque) appliedfrom the input shaft on the steering wheel side according to thesteering operation, reaction force from road surface applied on a wheelfor steering acts on the steering shaft of a running vehicle as an inputtorque (called “inverse input torque” in the following) from the outputshaft on the steering mechanism side. For example, at straight drivingwithout turning the steering wheel, when the vehicle runs on rough roadsurface and large inverse input torque is applied, the inverse inputtorque may be detected by the torque detecting apparatus constructed asdescribed above.

[0011] Inverse input torque is applied such that the rotation of theoutput shaft side precedes that of the input shaft side, while theproper steering torque is applied such that the rotation of the inputshaft side precedes that of the output shaft side. Consequently, injudging the torque direction based on the detecting result by the torquedetecting apparatus, the inverse input torque is judged to be steeringtorque applied in the direction, in which the wheel for steering isenergized by the action of the reaction force from the road surface.When the steering force assisting motor is driven according to such atorque detection, driving force of the motor is applied on the steeringmechanism in the same direction as the inverse input torque, and thedriver who is at the wheel feels such that the primary inverse inputtorque is promoted. The conventional art thus has a problem of causing adeterioration of a steering feeling.

BRIEF SUMMARY OF THE INVENTION

[0012] The present invention has been made to solve the problematicpoint mentioned above.

[0013] One object of the present invention is to provide a torquedetecting apparatus for detecting steering torque applied on thesteering shaft, which connects the steering wheel and the steeringmechanism, from the steering wheel side, and inverse input torqueapplied on the steering shaft from the steering mechanism side,separately.

[0014] Another object of the invention is to provide an electric powersteering apparatus which can prevent the deterioration of steeringfeeling when the inverse input torque acts, by driving the steeringforce assisting motor in a direction to cancel the inverse input torque,or by not driving the steering force assisting motor.

[0015] A torque detecting apparatus according to the present inventionjudges that inverse input torque is applied on a steering shaft whichconnects the steering wheel and the steering mechanism, when apredetermined interrelation exists among vehicle speed and two angularvelocities which are calculated at two positions distant in the axialdirection of the steering shaft. The torque detecting apparatus attemptsto prevent inappropriate controlling operation by outputting torque ofassistance force calculated in a predetermined way as follows. When theinverse input torque acts, the torque of assistance force is calculatedby inverting the direction of the detected torque or by inverting thedirection of torque obtained by multiplying the detected torque, orfixed zero.

[0016] An electric power steering apparatus according to the presentinvention attempts to prevent the deterioration of steering feelingcaused by the action of the inverse input torque. The electric powersteering apparatus detects the proper steering torque and the inverseinput torque separately in the same way as the torque detectingapparatus, and, when the inverse input torque is detected, drives thesteering force assisting motor in the opposite direction to the detectedtorque direction according to the torque of assistance force, which isoutput by the torque detecting apparatus, or does not drive the motor.

[0017] These and other objects, features and advantages of the inventionwill become more apparent upon a reading of the following detaileddescription and drawing.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0018]FIG. 1 is a schematic representation of an electric power steeringapparatus provided with a torque detecting apparatus according to thepresent invention;

[0019]FIG. 2 is a graph showing an example of output voltage change of amagnetometric sensor;

[0020]FIG. 3 is a flow chart showing operational content of adrive-control unit according to Example 1;

[0021]FIG. 4 is a view illustrating an example of a discriminant map fordiscriminating calculated torque;

[0022]FIG. 5 is a flow chart showing operational content of adrive-control unit according to Example 2; and

[0023]FIG. 6 is a flow chart showing operational content of adrive-control unit according to Example 3.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, the present invention is concretely described on thebasis of the drawings which show the embodiments thereof.

[0025]FIG. 1 is a schematic representation of an electric power steeringapparatus provided with a torque detecting apparatus according to thepresent invention. As shown in the figure, an input shaft 31 connectedat the upper end thereof to a steering wheel 30 for steering operationand an output shaft 32 connected to a pinion 40 of a steering mechanism4 described below are connected through a torsion bar 33 of a smalldiameter to construct a steering shaft 3 which connects the steeringwheel 30 and the steering mechanism 4.

[0026] The steering mechanism 4 is constructed as a steering mechanismof a rack and pinion type having the pinion 40 and a rack shaft 41geared with the pinion 40. The rack shaft 41 is extended in right andleft direction of a vehicle which is unshown and is connected to wheelsfor steering 43, 43 (wheels for steering are generally front wheels)through each of tie rods 42, 42 at the right and left ends thereof. Inthis construction, turning the steering wheel 30 generates the rotationof the pinion 40 and the rotation transmitted through the steering shaft3 is then converted into axial directional movement of the rack shaft 41geared with the pinion 40. The movement of the rack shaft 41 istransmitted to wheels for steering 43, 43 through the tie rods 42, 42,and the direction of the wheel 43, 43 is controlled.

[0027] The steering mechanism 4 is constructed as an electric powersteering apparatus for assisting the steering operation mentioned aboveby a steering force assisting motor M. The steering force assistingmotor M is provided in the middle of the steering shaft 3 and a worm 34fitted to an output terminal of the motor M is geared with a worm wheel35 which is fixed to the middle of the output shaft 32. In thisconstruction, rotation of the motor M is transmitted to the output shaft32 through the worm 34 and the worm wheel 35, and the torque is grantedto the pinion 40 connected to the lower end of the output shaft 32.Steering is assisted according to said rotation.

[0028] A torque detecting apparatus according to the present inventionis constructed in proximity to a connection part of the input shaft 31and the output shaft 32 as described below, to detect the steeringtorque applied on the steering shaft 3 by the operation of the steeringwheel 30.

[0029] A discoid target ring 2, which has integrally molded plurality oftarget gears 20, 20 . . . (FIG. 1 shows ten) thereon, is coaxially fixedto the input shaft 31 in proximity to the connection part with theoutput shaft 32. The target gears 20, 20 . . . are magnetic protrusionstilted at an approximately same angle in the same direction against theaxial direction of the input shaft 31 to which the target ring 2 isfixed. The target gears 20, 20 . . . are arranged at regular intervalsin a peripheral direction of the target ring 2.

[0030] The same target ring 2 is also fixed to the output shaft 32 inproximity to the connection part with the input shaft 31. The targetring 2 has, on the periphery thereof, plurality of target gears 20, 20 .. . tilted at an approximately same angle against the axial direction ofthe output shaft 32 to which the target ring 2 is fixed. The peripheralpositions of the target gears 20, 20 . . . on the output shaft 32 areadjusted to the positions of the target gears 20, 20 . . . on the inputshaft 31.

[0031] Two sensor boxes 1 a, 1 b are provided on the exterior of thetarget rings 2, 2, facing the arranged position of each set of targetgears 20, 20 . . . from peripherally different positions. The sensorboxes 1 a, 1 b are fitted to a stable part such as a housing forsupporting the input shaft 31 and the output shaft 32. A magnetometricsensor 1A facing the target gears 20, 20 . . . at the input shaft 31side and a magnetometric sensor 1B facing the target gears 20, 20 . . .at the output shaft 32 side are disposed in the sensor box 1 a,peripheral directions thereof being adjusted. Also, a magnetometricsensor 2A facing the target gears 20, 20 . . . at the input shaft 31side and a magnetometric sensor 2B facing the target gears 20, 20 . . .at the output shaft 32 side are disposed in the sensor box 1 b,peripheral directions thereof being adjusted.

[0032] The magnetometric sensors 1A, 1B, 2A, 2B are constructed tochange output voltage according to the change of a peripheral magneticfield, using an element which changes an electrical characteristicthereof by the action of the magnetic field, such as a magnetoresistanceeffect element (MR element). Outputs V_(1A), V_(1B), V_(2A), V_(2B) ofthe magnetometric sensors 1A, 1B, 2A, 2B are transmitted from the sensorboxes 1 a, 1 b to a drive-control unit 5 comprising a microprocessor.

[0033]FIG. 2 is a graph showing an example of output voltage change ofmagnetometric sensors 1A, 1B, 2A, 2B. The axis of abscissas shows arotational angle of the input shaft 31 or the output shaft 32. A fullline in the figure shows the output voltage V_(1A), V_(2A) of themagnetometric sensors 1A, 2A at the input shaft 31 side, while a brokenline in the figure shows the output voltage V_(1B), V_(2B) of themagnetometric sensors 1B, 2B at the output shaft 32 side.

[0034] As mentioned above, the target gears 20, 20 . . . , which themagnetometric sensors 1A, 1B, 2A, 2B face, are magnetic protrusionstilted at an approximately same angle in the same direction against theaxial direction of the input shaft 31 and the output shaft 32, and adiscontinuous part exists between each two target gears 20, 20. So, whenthe input shaft 31 and the output shaft 32 rotates on an axis thereof,each of magnetometric sensors 1A, 1B, 2A, 2B outputs a voltage signalwhich changes linearly according to the change of the rotational angleof the input shaft 31 or the output shaft 32 when corresponding targetgears 20, 20 . . . pass by, and outputs a voltage signal which changesnonlinearly according to the change of said rotational angle when thediscontinuous parts pass by.

[0035] As a result, the output voltage of the magnetometric sensors 1A,1B, 2A, 2B includes a region in which the output voltage changeslinearly when each target gear 20 passes (a linear change region) and aregion in which the output voltage changes nonlinearly when thediscontinuous part between target gears 20, 20 passes (a nonlinearchange region), the linear change region and the nonlinear change regionshowing up reciprocally and repeatedly as shown in FIG. 2. A period ofthe repetition of the linear change region and the nonlinear changeregion corresponds to the number of the target gears 20, 20 . . .arranged on the periphery of the target ring 2. When ten target gears20, 20 . . . are arranged on the periphery of the target ring 2, arisesa repetition with a period corresponding to the rotational angle of 36°(=360°/10) of the input shaft 31 or the output shaft 32.

[0036] The output voltages V_(1A), V_(2A) of the magnetometric sensors1A, 2A corresponds to the rotational angle of the input shaft 31provided with the target gears 20, 20 . . . which the sensors 1A, 2Aface, while the output voltages V_(1B), V_(2B) of the magnetometricsensors 1B, 2B correspond to the rotational angle of the output shaft 32provided with the target gears 20, 20 . . . which the sensors 1B, 2Bface. A difference ΔV₁ between the output voltage V_(1A) of themagnetometric sensor 1A and the output voltage V_(1B) of themagnetometric sensor 1B (=V_(1A)-V_(1B)), or a difference ΔV₂ betweenthe output voltage V_(2A) of the magnetometric sensor 2A and the outputvoltage V_(2B) of the magnetometric sensor 2B (=V_(2A)-V_(2B))corresponds to displacement amount in the peripheral direction (relativeangle displacement) which arises between the target gears 20, 20 . . .at the input shaft 31 side and the target gears 20, 20 . . . at theoutput shaft 32 side. The relative angle displacement corresponds totorsion amount of a torsion bar 33 connecting the input shaft 31 and theoutput shaft 32, generated by the action of the steering torque appliedon the input shaft 31. Consequently, the steering torque applied on theinput shaft 31 can be calculated based on the difference between theoutput voltages ΔV₁ or ΔV₂.

[0037] Such calculation of the steering torque is performed at thedrive-control unit 5 to which the output voltages of the magnetometricsensors 1A, 1B, 2A, 2B are granted. Calculation steps are fullydescribed in the Unexamined Japanese Patent Publication No. 2000-352502by the present applicant and omitted here. In short, the magnitude ofthe steering torque is calculated based on an absolute value of thedifference between the output voltages ΔV₁ or ΔV₂, and a direction ofthe steering torque is judged based on the plus and minus sign of theΔV₁ or ΔV₂.

[0038] Two pairs of magnetometric sensors 1A, 2A and 1B, 2B are arrangedon the exterior of the target gears 20, 20 . . . at the input shaft 31side and the output shaft 32 side to avoid outputting incorrect steeringtorque using an unreliable output at the nonlinear change region shownin FIG. 2. Two magnetometric sensors 1A, 1B in one sensor box 1 a andtwo magnetometric sensors 2A, 2B in the other sensor box 1 b are setwith phases thereof shifted in the peripheral direction. In thisconstruction, when one pair of outputs (V_(1A), V_(1B)) are in thenonlinear change region, the other pair of outputs (V_(2A), V_(2B)) arein the linear change region. One pair, the outputs of which are in thelinear change region, is selected from the magnetometric sensors 1A, 1Band the magnetometric sensors 2A, 2B, and steering torque is calculatedbased on the output difference of the selected pair, at thedrive-control unit 5.

[0039] The output from the drive-control unit 5 is transmitted to thesteering force assisting motor M which is provided in the middle of theoutput shaft 32 as mentioned above. The drive-control unit 5 basicallyassists steering by driving the motor M to generate turning effort inthe same direction as the calculated steering torque, according to themagnitude of the steering torque. As described above, the turning effortof the motor M is transmitted to the output shaft 32 through the worm 34and the worm wheel 35. Steering assistance is achieved when the turningeffort is applied to the pinion 40 disposed at the lower end of theoutput shaft 32.

[0040] However, torque calculation is performed not only for the propersteering torque applied from the input shaft 31 side according to theoperation of the steering wheel 30 but also for the inverse input torqueapplied from the output shaft 32 side according to the reaction forcefrom the road surface to the wheels for steering 43, 43 as mentionedabove. When the steering force assisting motor is driven based on thecalculated inverse input torque, the inverse input torque is promoted bythe turning effort which is applied on the steering mechanism by themotor M. Such a promotion may cause a deterioration of steering feeling.

[0041] The drive-control unit 5 is constructed to discriminate whetheran output voltage transmitted from the magnetometric sensors 1A, 1B, 2A,2B is an output voltage generated by the proper steering torque or anoutput voltage generated by the inverse input torque, and to drive andcontrol the motor M according to the discrimination result. Output froma speed sensor 6 for detecting vehicle speed is also applied to theinput side of the drive-control unit 5. The vehicle speed detected bythe speed sensor 6 is used for the torque discrimination.

[0042]FIG. 3 is a flow chart showing the operational content of adrive-control unit 5 according to Example 1. The drive-control unit 5starts operation on response to power supply by turning a key switch on,and fetches the output voltage V_(1A), V_(1B) of the magnetometricsensors 1A, 1B and the output voltage V_(2A), V_(2B) of themagnetometric sensors 2A, 2B, for a predetermined sampling period (STEP1). The drive-control unit 5 calculates torque T applied on the steeringshaft 3 based on an output difference ΔV₁ or ΔV₂ which is in a linearchange region.

[0043] The drive-control unit 5 checks whether the torque T calculatedin STEP 2 is within a predetermined dead zone ΔT (STEP 3). When thecalculated torque T is within the dead zone ΔT, the procedure isreturned to STEP 1 without performing steps described below, and fetchesthe next output voltage.

[0044] When the calculated torque T is beyond the dead zone ΔT, thedrive-control unit 5 fetches an output from the speed sensor 6 connectedto the input side, calculates existing vehicle speed (STEP 4), andcalculates angular velocities ω₁ and ω₂ of the input shaft 31 and theoutput shaft 32 based on the output voltages of the magnetometricsensors used for calculating the steering torque, e.g. the outputvoltages V_(1A), V_(1B) of the magnetometric sensors 1A, 1B (STEP 5). Byapplying such a calculation result and the vehicle speed to anpredetermined map, the drive-control unit 5 discriminates whether thecalculated torque T is steering torque applied from the steering wheel30 side or inverse input torque applied from the steering mechanism 4side (STEP 6).

[0045] The output voltages V_(1A), V_(1B) of the magnetometric sensors1A, 1B correspond to the rotational angles of the input shaft 31 and theoutput shaft 32, which the magnetometric sensors 1A, 1B are set to face,and the angular velocities ω₁ and ω₂ are readily calculated bydifferentiating the output voltages V_(1A), V_(1B) by time.

[0046]FIG. 4 is a view illustrating an example of a discriminant map fordiscriminating the torque T calculated in STEP 6. As shown in thefigure, the discriminant map expresses, on three-dimensional coordinateaxes, three variables: an angular velocity of the input shaft 31; anangular velocity of the output shaft 32; and the vehicle speed. Thediscrimination is performed by applying a state point decided with acombination of the angular velocities ω₁ and ω₂ calculated in STEP 5 andthe vehicle speed v detected in STEP 4 to a predetermined map, andchecking whether or not the state point is within an inverse inputregion A which is hatched in the figure, for example. When the statepoint is beyond the inverse input region A, the calculated torque T isdiscriminated to be steering torque applied on the steering wheel 30 forsteering, while when the state point is within the inverse input regionA, the calculated torque T is discriminated to be inverse input torqueapplied from the steering mechanism 4 side by the action of disturbanceforce such as the reaction force from the road surface.

[0047] The inverse input region A covers cases where the vehicle speed vis relatively high and the angular velocity ω₂ of the output shaft 32side is greater than the angular velocity ω₁ of the input shaft 31 side.When inverse input torque is generated by disturbance force such asreaction force from the road surface, the output shaft 32 rotates aheadof the input shaft 31 in a direction of the inverse input torque. Theoutput shaft 32 also rotates ahead of the input shaft 31 when steeringtorque is generated by turning the steering wheel 30 in the oppositedirection.

[0048] A difference between the two situations mentioned above is: whensteering torque acts, the angular velocity of the input shaft 31 isgreater than the angular velocity of the output shaft 32; while wheninverse input torque acts, the angular velocity of the output shaft 32,which is an input side of the inverse input torque, is greater than theangular velocity of the input shaft 31. The inverse input region A setbased on the difference enables the discrimination of the detectedtorque T.

[0049] The inverse input region A is set only for the cases where thevehicle speed is high because deterioration of steering feeling causedby the inverse input torque comes to the front only at high vehiclespeed driving. It is preferable that a practical inverse input region Ais decided on reference to a result of driving test carried on an actualvehicle.

[0050] When the calculated torque T is discriminated to be steeringtorque in STEP 6, the calculated torque T is set as torque of assistanceforce T_(o) (STEP 7), while when the calculated torque T isdiscriminated to be inverse input torque, torque with an opposite signto the calculated torque T is set as torque of assistance force T_(o)(STEP 8). The drive-control unit 5 gives an instruction for operation tothe steering force assisting motor M and drives the motor M, to generateassistance force in the direction of the torque of assistance forceT_(o) (STEP 9). The procedure is then returned to STEP 1.

[0051] In steps described above, when inverse input torque acts, thesteering force assisting motor M is driven in a direction to cancel theinverse input torque. At straight driving without turning the steeringwheel, for example, such motor drive softens bodily sensation of theinverse input torque by the action of disturbance force from the roadsurface. The above mentioned steps thus realize satisfactory steeringfeeling.

[0052]FIG. 5 is a flow chart showing the operational content of adrive-control unit 5 according to Example 2. In FIG. 5, like stepnumbers are used to refer to like steps shown in FIG. 3. At adrive-control unit 5 according to Example 2, torque of assistance forceT_(o) is decided by multiplying the calculated torque T by a coefficientk besides inverting the sign of the calculated torque T (STEP 18) wheninverse input torque is detected. The cancellation of the inverse inputtorque is controlled to be positive or negative by changing thecoefficient k.

[0053]FIG. 6 is a flow chart showing the operational content of adrive-control unit 5 according to Example 3. In FIG. 6, like stepnumbers are used to refer to like steps shown in FIG. 3. At adrive-control unit 5 according to Example 3, torque of assistance forceT₀ is always set at zero (STEP 28) when inverse input torque isdetected. The steering force assisting motor M is thus not driven wheninverse input torque acts.

[0054] Though a torque detecting apparatus proposed in the UnexaminedJapanese Patent Publication No. 2000-352502 by the present applicant isused in above embodiments, the present invention is applicable to theall torque detecting apparatus which are constructed to calculatesteering torque based on a difference between rotational angles detectedrespectively at two positions on the steering shaft 3.

[0055] It is further understood by those skilled in the art that theforegoing description is a preferred embodiment of the disclosed deviceand that various changes and modifications may be made in the inventionwithout departing from the spirit and scope thereof.

[0056] As this invention may be embodied in several forms withoutdeparting from the spirit of essential characteristics thereof, thepresent embodiment is therefore illustrative and not restrictive, sincethe scope of the invention is defined by the appended claims rather thanby the description preceding them, and all changes that fall withinmetes and bounds of the claims, or equivalence of such metes and boundsthereof are therefore intended to be embraced by the claims.

1. A torque detecting apparatus, comprising: a first rotational anglesensor and a second rotational angle sensor for detecting rotationalangles of a steering shaft, which connects a steering mechanism and asteering wheel of a vehicle, at two positions distant in axial directionof the steering shaft; torque calculating means for calculating amagnitude and a direction of steering torque applied on the steeringwheel, based on a difference between the rotational angles detected bythe first rotational angle sensor and the second rotational anglesensor; a speed sensor for detecting a vehicle speed; angular velocitycalculating means for calculating angular velocities of the steeringshaft at the respective detection positions thereof, based on detectionresults of the first rotational angle sensor and the second rotationalangle sensor; discrimination means for discriminating whether or not apredetermined interrelation exists among the angular velocitiescalculated by the angular velocity calculating means and the vehiclespeed detected by the speed sensor; and means for inverting thedirection of the steering torque calculated by the torque calculatingmeans, when the predetermined interrelation is discriminated to exist bythe discrimination means.
 2. A torque detecting apparatus according toclaim 1, wherein the angular velocity calculating means calculates theangular velocities of the input shaft and the output shaft bydifferentiating, by time, outputs of the first rotational angle sensorand the second rotational angle sensor respectively.
 3. A torquedetecting apparatus according to claim 1, wherein the discriminationmeans discriminates whether the detected torque is steering torqueapplied on the steering wheel or inverse input torque caused bydisturbance force, by applying a state point decided by a combination ofthe calculated angular velocities and the detected vehicle speed to adiscriminant map expressing, on three-dimensional coordinate axes, threevariables: an angular velocity of the input shaft; an angular velocityof the output shaft; and the vehicle speed.
 4. A torque detectingapparatus, comprising: a first rotational angle sensor and a secondrotational angle sensor for detecting rotational angles of a steeringshaft, which connects a steering mechanism and a steering wheel of avehicle, at two positions distant in axial direction of the steeringshaft; a torque calculator for calculating a magnitude and a directionof steering torque applied on the steering wheel, based on a differencebetween the rotational angles detected by the first rotational anglesensor and the second rotational angle sensor; a speed sensor fordetecting a vehicle speed; an angular velocity calculator forcalculating angular velocities of the steering shaft at the respectivedetection positions thereof, based on detection results of the firstrotational angle sensor and the second rotational angle sensor; adiscrimination unit for discriminating whether or not a predeterminedinterrelation exists among the angular velocities calculated by theangular velocity calculator and the vehicle speed detected by the speedsensor; and a control unit for inverting the direction of the steeringtorque calculated by the torque calculator, when the predeterminedinterrelation is discriminated to exist by the discrimination unit.
 5. Atorque detecting apparatus according to claim 4, wherein the angularvelocity calculator calculates the angular velocities of the input shaftand the output shaft by differentiating, by time, outputs of the firstrotational angle sensor and the second rotational angle sensorrespectively.
 6. A torque detecting apparatus according to claim 4,wherein the discrimination unit discriminates whether the detectedtorque is steering torque applied on the steering wheel or inverse inputtorque caused by disturbance force, by applying a state point decided bya combination of the calculated angular velocities and the detectedvehicle speed to a discriminant map expressing, on three-dimensionalcoordinate axes, three variables: an angular velocity of the inputshaft; an angular velocity of the output shaft; and the vehicle speed.7. An electric power steering apparatus, comprising: a first rotationalangle sensor and a second rotational angle sensor for detectingrotational angles of a steering shaft, which connects a steeringmechanism and a steering wheel of a vehicle, at two positions distant inaxial direction of the steering shaft; torque calculating means forcalculating a magnitude and a direction of steering torque applied onthe steering wheel, based on a difference between the rotational anglesdetected by the first rotational angle sensor and the second rotationalangle sensor; means for driving and controlling a steering forceassisting motor provided to the steering mechanism, to apply assistanceforce to the steering mechanism according to a direction and a magnitudeof calculated steering torque; a speed sensor for detecting a vehiclespeed; angular velocity calculating means for calculating angularvelocities of the steering shaft at the respective detection positionsthereof, based on detection results of the first rotational angle sensorand the second rotational angle sensor; discrimination means fordiscriminating whether or not a predetermined interrelation exists amongthe angular velocities calculated by the angular velocity calculatingmeans and the vehicle speed detected by the speed sensor; and means forinverting a driving direction of the motor which is decided based on adetection result of the steering torque, when the predeterminedinterrelation is discriminated to exist by the discrimination means. 8.An electric power steering apparatus according to claim 7, wherein theangular velocity calculating means calculates the angular velocities ofthe input shaft and the output shaft by differentiating, by time,outputs of the first rotational angle sensor and the second rotationalangle sensor respectively.
 9. An electric power steering apparatusaccording to claim 7, wherein the discrimination means discriminateswhether the detected torque is steering torque applied on the steeringwheel or inverse input torque caused by disturbance force, by applying astate point decided by a combination of the calculated angularvelocities and the detected vehicle speed to a discriminant mapexpressing, on three-dimensional coordinate axes, three variables: anangular velocity of the input shaft; an angular velocity of the outputshaft; and the vehicle speed.
 10. An electric power steering apparatus,comprising: a first rotational angle sensor and a second rotationalangle sensor for detecting rotational angles of a steering shaft, whichconnects a steering mechanism and a steering wheel of a vehicle, at twopositions distant in axial direction of the steering shaft; a torquecalculator for calculating a magnitude and a direction of steeringtorque applied on the steering wheel, based on a difference between therotational angles detected by the first rotational angle sensor and thesecond rotational angle sensor; a drive-control unit for driving andcontrolling a steering force assisting motor provided to the steeringmechanism, to apply assistance force to the steering mechanism accordingto a direction and a magnitude of calculated steering torque; a speedsensor for detecting a vehicle speed; an angular velocity calculator forcalculating angular velocities of the steering shaft at the respectivedetection positions thereof, based on detection results of the firstrotational angle sensor and the second rotational angle sensor; adiscrimination unit for discriminating whether or not a predeterminedinterrelation exists among the angular velocities calculated by theangular velocity calculator and the vehicle speed detected by the speedsensor; and a control unit for inverting a driving direction of themotor which is decided based on a detection result of the steeringtorque, when the predetermined interrelation is discriminated to existby the discrimination unit.
 11. An electric power steering apparatusaccording to claim 10, wherein the angular velocity calculatorcalculates the angular velocities of the input shaft and the outputshaft by differentiating, by time, outputs of the first rotational anglesensor and the second rotational angle sensor respectively.
 12. Anelectric power steering apparatus according to claim 10, wherein thediscrimination unit discriminates whether the detected torque issteering torque applied on the steering wheel or inverse input torquecaused by disturbance force, by applying a state point decided by acombination of the calculated angular velocities and the detectedvehicle speed to a discriminant map expressing, on three-dimensionalcoordinate axes, three variables: an angular velocity of the inputshaft; an angular velocity of the output shaft; and the vehicle speed.13. A torque detecting apparatus, comprising: a first rotational anglesensor and a second rotational angle sensor for detecting rotationalangles of a steering shaft, which connects a steering mechanism and asteering wheel of a vehicle, at two positions distant in axial directionof the steering shaft; torque calculating means for calculating amagnitude and a direction of steering torque applied on the steeringwheel, based on a difference between the rotational angles detected bythe first rotational angle sensor and the second rotational anglesensor; a speed sensor for detecting a vehicle speed; angular velocitycalculating means for calculating angular velocities of the steeringshaft at the respective detection positions thereof, based on detectionresults of the first rotational angle sensor and the second rotationalangle sensor; discrimination means for discriminating whether or not apredetermined interrelation exists among the angular velocitiescalculated by the angular velocity calculating means and the vehiclespeed detected by the speed sensor; and means for inverting thedirection of the steering torque calculated by the torque calculatingmeans and multiplying the steering torque by an appropriate coefficient,when the predetermined interrelation is discriminated to exist by thediscrimination means.
 14. A torque detecting apparatus, comprising:first rotational angle sensor and a second rotational angle sensor fordetecting rotational angles of a steering shaft, which connects asteering mechanism and a steering wheel of a vehicle, at two positionsdistant in axial direction of the steering shaft; a torque calculatorfor calculating a magnitude and a direction of steering torque appliedon the steering wheel, based on a difference between the rotationalangles detected by the first rotational angle sensor and the secondrotational angle sensor; a speed sensor for detecting a vehicle speed;an angular velocity calculator for calculating angular velocities of thesteering shaft at the respective detection positions thereof, based ondetection results of the first rotational angle sensor and the secondrotational angle sensor; a discrimination unit for discriminatingwhether or not a predetermined interrelation exists among the angularvelocities calculated by the angular velocity calculator and the vehiclespeed detected by the speed sensor; and a control unit for inverting thedirection of the steering torque calculated by the torque calculator andmultiplying the steering torque by an appropriate coefficient, when thepredetermined interrelation is discriminated to exist by thediscrimination unit.
 15. An electric power steering apparatus,comprising: a first rotational angle sensor and a second rotationalangle sensor for detecting rotational angles of a steering shaft, whichconnects a steering mechanism and a steering wheel of a vehicle, at twopositions distant in axial direction of the steering shaft; torquecalculating means for calculating a magnitude and a direction ofsteering torque applied on the steering wheel, based on a differencebetween the rotational angles detected by the first rotational anglesensor and the second rotational angle sensor; means for driving andcontrolling a steering force assisting motor provided to the steeringmechanism, to apply assistance force to the steering mechanism accordingto a direction and a magnitude of calculated steering torque; a speedsensor for detecting a vehicle speed; angular velocity calculating meansfor calculating angular velocities of the steering shaft at therespective detection positions thereof, based on detection results ofthe first rotational angle sensor and the second rotational anglesensor; discrimination means for discriminating whether or not apredetermined interrelation exists among the angular velocitiescalculated by the angular velocity calculating means and the vehiclespeed detected by the speed sensor; and means for inverting a drivingdirection of the motor which is decided based on a detection result ofthe steering torque and multiplying the calculated steering torque by anappropriate coefficient to give a torque of assistance force, when thepredetermined interrelation is discriminated to exist by thediscrimination means.
 16. An electric power steering apparatus,comprising: first rotational angle sensor and a second rotational anglesensor for detecting rotational angles of a steering shaft, whichconnects a steering mechanism and a steering wheel of a vehicle, at twopositions distant in axial direction of the steering shaft; a torquecalculator for calculating a magnitude and a direction of steeringtorque applied on the steering wheel, based on a difference between therotational angles detected by the first rotational angle sensor and thesecond rotational angle sensor; a drive-control unit for driving andcontrolling a steering force assisting motor provided to the steeringmechanism, to apply assistance force to the steering mechanism accordingto a direction and a magnitude of the calculated steering torque; aspeed sensor for detecting a vehicle speed; an angular velocitycalculator for calculating angular velocities of the steering shaft atthe respective detection positions thereof, based on detection resultsof the first rotational angle sensor and the second rotational anglesensor; a discrimination unit for discriminating whether or not apredetermined interrelation exists among the angular velocitiescalculated by the angular velocity calculator and the vehicle speeddetected by the speed sensor; and a control unit for inverting a drivingdirection of the motor which is decided based on a detection result ofthe steering torque and multiplying the calculated steering torque by anappropriate coefficient to give a torque of assistance force, when thepredetermined interrelation is discriminated to exist by thediscrimination means.
 17. A torque detecting apparatus, comprising: afirst rotational angle sensor and a second rotational angle sensor fordetecting rotational angles of a steering shaft, which connects asteering mechanism and a steering wheel of a vehicle, at two positionsdistant in axial direction of the steering shaft; torque calculatingmeans for calculating a magnitude and a direction of steering torqueapplied on the steering wheel, based on a difference between therotational angles detected by the first rotational angle sensor and thesecond rotational angle sensor; a speed sensor for detecting a vehiclespeed; angular velocity calculating means for calculating angularvelocities of the steering shaft at the respective detection positionsthereof, based on detection results of the first rotational angle sensorand the second rotational angle sensor; discrimination means fordiscriminating whether or not a predetermined interrelation exists amongthe angular velocities calculated by the angular velocity calculatingmeans and the vehicle speed detected by the speed sensor; and means forsetting a torque of assistance force at zero, when the predeterminedinterrelation is discriminated to exist by the discrimination means. 18.A torque detecting apparatus, comprising: a first rotational anglesensor and a second rotational angle sensor for detecting rotationalangles of a steering shaft, which connects a steering mechanism and asteering wheel of a vehicle, at two positions distant in axial directionof the steering shaft; a torque calculator for calculating a magnitudeand a direction of steering torque applied on the steering wheel, basedon a difference between the rotational angles detected by the firstrotational angle sensor and the second rotational angle sensor; a speedsensor for detecting a vehicle speed; an angular velocity calculator forcalculating angular velocities of the steering shaft at the respectivedetection positions thereof, based on detection results of the firstrotational angle sensor and the second rotational angle sensor; adiscrimination unit for discriminating whether or not a predeterminedinterrelation exists among the angular velocities calculated by theangular velocity calculator and the vehicle speed detected by the speedsensor; and a control unit for setting a torque of assistance force atzero, when the predetermined interrelation is discriminated to exist bythe discrimination unit.
 19. An electric power steering apparatus,comprising: a first rotational angle sensor and a second rotationalangle sensor for detecting rotational angles of a steering shaft, whichconnects a steering mechanism and a steering wheel of a vehicle, at twopositions distant in axial direction of the steering shaft; torquecalculating means for calculating a magnitude and a direction ofsteering torque applied on the steering wheel, based on a differencebetween the rotational angles detected by the first rotational anglesensor and the second rotational angle sensor; means for driving andcontrolling a steering force assisting motor provided to the steeringmechanism, to apply assistance force to the steering mechanism accordingto a direction and a magnitude of the calculated steering torque; aspeed sensor for detecting a vehicle speed; angular velocity calculatingmeans for calculating angular velocities of the steering shaft at therespective detection positions thereof, based on detection results ofthe first rotational angle sensor and the second rotational anglesensor; discrimination means for discriminating whether or not apredetermined interrelation exists among the angular velocitiescalculated by the angular velocity calculating means and the vehiclespeed detected by the speed sensor; and means for suspending motordrive, when the predetermined interrelation is discriminated to exist bythe discrimination means.
 20. An electric power steering apparatus,comprising: a first rotational angle sensor and a second rotationalangle sensor for detecting rotational angles of a steering shaft, whichconnects a steering mechanism and a steering wheel of a vehicle, at twopositions distant in axial direction of the steering shaft; a torquecalculator for calculating a magnitude and a direction of steeringtorque applied on the steering wheel, based on a difference between therotational angles detected by the first rotational angle sensor and thesecond rotational angle sensor; a drive-control unit for driving andcontrolling a steering force assisting motor provided to the steeringmechanism, to apply assistance force to the steering mechanism accordingto a direction and a magnitude of the calculated steering torque; aspeed sensor for detecting a vehicle speed; an angular velocitycalculator for calculating angular velocities of the steering shaft atthe respective detection positions thereof, based on detection resultsof the first rotational angle sensor and the second rotational anglesensor; a discrimination unit for discriminating whether or not apredetermined interrelation exists among the angular velocitiescalculated by the angular velocity calculator and the vehicle speeddetected by the speed sensor; and a control unit for suspending motordrive, when the predetermined interrelation is discriminated to exist bythe discrimination unit.